If you redistribute or screen or broadcast the movie itself: include the entire credits scroll.

In all other cases, attribute it as: (c) copyright Blender Foundation | www.bigbuckbunny.org

This is the first time such a large collection of files get launched under ‘the commons’, and therefore still a bit complex to grasp what to credit when exactly. The guidelines above are just meant to ensure that attribution happens in a reasonable way. If in doubt, use the second choice above.